e2mmpstatus — Check MMP status of an ext4 filesystem
Synopsis
e2mmpstatus [-i] <filesystem>
Options
- -i
prints out the MMP information rather than check it.
Description
e2mmpstatus is used to check Multiple-Mount Protection (MMP) status of an ext4 filesystem with the mmp feature enabled. The specified filesystem can be a device name (e.g. /dev/hdc1, /dev/sdb2), or an ext4 filesystem label or UUID, for example UUID=8868abf6-88c5-4a83-98b8-bfc24057f7bd or LABEL=root. By default, the e2mmpstatus program checks whether it is safe to mount the filesystem without taking the risk of mounting it more than once.
MMP (multiple-mount protection) is a feature that adds protection against the filesystem being modified simultaneously by more than one node. It is NOT safe to mount a filesystem when one of the following conditions is true:
1. e2fsck is running on the filesystem.
2. the filesystem is in use by another node.
3. The MMP block is corrupted or cannot be read for some reason.
The e2mmpstatus program might wait for some time to see whether the MMP block is being updated by any node during this period. The time taken depends on how frequently the MMP block is being written by the other node.
Exit Code
The exit code returned by e2mmpstatus is 0 when it is safe to mount the filesystem, 1 when the MMP block shows the filesystem is in use on another node and it is NOT safe to mount the filesystem, and 2 if some other failure occurred that prevents the check from properly detecting the current MMP status.